In optical communications, a single optical fiber may convey signals at different wavelengths. Furthermore, via a wavelength-selective switch, it is possible to add or remove one or more carriers onto or from the optical fiber.
Today, there are three predominant technologies for switching beams of light within a wavelength selective switch (WSS). These technologies are based on using a micro-electromechanical system (MEMS) array, Liquid-Crystal-on-Silicon (LCOS) array, and Liquid Crystal (LC) elements array. Independently of the switching technology used within a WSS, the optical path of the beam of light in the WSS passes through a diffractive structure that implements channel demultuplexing before a switching function. A switching element (MEMS, LCOS, or LC) that implements the switching function directs each channel to a designated output port.
In a WSS that uses the LCOS, each of pixels (e.g., liquid crystal cells on a flat surface) in an array is electronically and individually controlled, in a manner analogous to that in which an individual element in a phased array antenna is controlled to change the phase of the signal reflected from an antenna element. Each antenna element contributes a coherent component of far-field signal in a particular direction. With each liquid crystal cell acting analogous to a phase-changing antenna element, a LCOS device can steer beams in optical frequencies.